This invention relates to the contemporaneous acidification of alkali metal salicylate and the sublimation of the salicyclic acid product.
It has long been known in the prior art that salicylic acid can be purified by sublimation. See, for example, U.S. Pat. Nos. 1,987,282 and 1,987,301. However, in the prior art the heat required to sublime the salicylic acid is supplied from external sources in a step separate and distinct from the acidification of the alkali metal salicylate.
Generally, the prior art acidifies sodium salicylate in a liquid medium containing a mineral acid to prepare salicylic acid. The liquid medium readily dissipates the heat of the acidification reaction. The salicylic acid is collected, dried and sublimed. The heat required to sublime the acid is imparted by a stream of heated gas or other means. The inefficiency of this heat transfer necessitates the use of relatively high temperatures which can decompose some of the salicylic acid.
In view of the deficiencies in the foregoing prior art methods of subliming salicylic acid, it would be highly desirable to provide a method of sublimation which utilizes the heat generated in the acidification of the alkali metal salicylate.